#include <cstdio>
int main()
{
    freopen("in.txt","r",stdin);
    double a[12],sum=0.0;
    for (int i=0;i<12;i++)
    {
        scanf("%lf",&a[i]);
        sum+=a[i];
    }
    printf("$%.2f\n",sum/12.0);
    return 0;
}
